ATLANTA, Georgia (CNN) -- Dogs bred for the fighting pit have only one thing in their future: death. Fighting dogs may die in the ring or at the hands of their owners. If they are confiscated in a bust, they are almost always euthanized, experts say.

Of the 1.4 million dogs euthanized at shelters last year, roughly half were pit bull types, Merritt Clifton says.

Thursday is the deadline for owners to retrieve any of the 50 remaining pit bulls seized in April from the Virginia property of suspended Atlanta Falcons quarterback Michael Vick, who is accused of using them in vicious dogfights.

A federal judge is expected to issue a court order to euthanize the animals.

Officials and animal rights advocates agree that the dogs must lose this last battle for their lives because of their brutal training and risks to people and other animals.

"They're just not in any situation where they can be adopted," said Dr. Lauren Adams, a veterinarian with Emory Animal Hospital in Decatur, Georgia. "They can snap at any point."

Of the 1.4 million dogs euthanized at shelters last year, roughly half were pit bull types, according to the latest data from Merritt Clifton, editor of Animal People. The pit bull is not a breed but a type that includes American Pit Bull Terriers, American Staffordshire Terriers, Staffordshire Bull Terriers, and pit bull mixes, according to the Pit Bull Rescue Central Web site. Clifton and other experts estimate anywhere from 25 to 50 percent of pit bulls euthanized at shelters were fighting dogs.

"Those dogs have been bred for aggression. You can breed for certain physical traits, but you can also breed for behavioral characteristics," said Wayne Pacelle, president of the Humane Society of the United States.

Dogs that lose the fights often are abandoned at shelters, but not all of them make it that far. Owners sometimes kill the dogs that don't win. Court documents from the Vick case say "the losing dog was sometimes put to death by drowning, strangulation, hanging, gun shot, electrocution or some other method." Learn about the dark world of dogfighting »

"It's very difficult to deprogram that behavior once it is instilled," Pacelle said. "Even if you can do it to some degree, all it takes is one lapse in the animal's behaviors to kill another animal or exhibit some other type of aggression."

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Additionally, shelters face the threat of theft. In the United States, there are an estimated 40,000 people who are considered professional dogfighters and another 100,000 amateur "streetfighters," according to John Goodwin, an expert on animal fighting with HSUS. Those involved compete for prizes as high as $100,000, and confiscated pit bulls are extremely valuable.

Inside the overpopulated shelters, where it's survival of the most adoptable, shelters focus their limited resources on the dogs that stand a better chance of finding a home.

The stigma associated with pit bull types has victimized the "good" pit bulls, Pacelle said. In some shelters, as many as 60 percent of dogs are pit bull mixes. More than 90 percent of pit bulls in shelters -- fighters or not -- end up euthanized, said Clifton, who has been researching animal shelters for more than three decades.

In the early 1900s, pit bulls were characterized as "nanny dogs" because they were used by families to baby-sit their children.

"By the end of the century, they were these horrible, aggressive, fighting dog machines, and that's very unfortunate," said Ed Boks, general manager of Los Angeles Animal Services in California.

The secondary fighting market has contributed to over breeding of pit bulls, Clifton said. The market creates a place where people can sell dogs as disposable commodities -- like pigs or chickens -- at much lower prices than would be invested in a pet, he said. These disposable dogs are designed to fight until they can fight no more.

"It was back in the '70s, '80s and '90s when people discovered just how loving these animals are -- so loving that they would fight to the death to please their owners," Boks said.

Considering the risk the fighting dogs pose to shelters, potential owners and other animals, "they just don't have a chance," Clifton said.

"You can compare it to what happens with exotic cats and people who keep tigers in their backyard. It's not the tiger's fault, but you are still on the menu. They are victims, but you do have to treat them as animals that belong in maximum security."E-mail to a friend